Expandable reamers are typically employed for enlarging subterranean boreholes. Conventionally in drilling oil, gas, and geothermal wells, casing is installed and cemented to prevent the well bore walls from caving into the subterranean borehole while providing requisite shoring for subsequent drilling operations to achieve greater depths. Casing is also conventionally installed to isolate different formations, to prevent cross-flow of formation fluids, and to enable control of formation fluids and pressure as the borehole is drilled. To increase the depth of a previously drilled borehole, new casing is laid within and extended below the previous casing. While adding additional casing allows a borehole to reach greater depths, it has the disadvantage of narrowing the borehole. Narrowing the borehole restricts the diameter of any subsequent sections of the well because the drill bit and any further casing must pass through the existing casing. As reductions in the borehole diameter are undesirable because they limit the production flow rate of oil and gas through the borehole, it is often desirable to enlarge a subterranean borehole to provide a larger borehole diameter for installing additional casing beyond previously installed casing as well as to enable better production flow rates of hydrocarbons through the borehole.
A variety of approaches have been employed for enlarging a borehole diameter. One conventional approach, as generally described in U.S. Pat. No. 7,036,611 entitled “Expandable Reamer Apparatus for Enlarging Boreholes While Drilling and Methods of Use,” the entire disclosure of which is incorporated by reference herein, provides for displacing an actuation sleeve allowing hydraulic fluid pressure to be directed at actuating laterally movable blades for reaming a borehole. The actuation sleeve is releasably restrained within an inner bore of an expandable reamer apparatus by way of shear pins, interlocking members, frictional elements, or friable members, and includes a fluid flow path through a sleeve seat. The fluid flow path is interrupted when a restriction element, such as a so-called “drop ball,” is deployed upon the sleeve seat allowing hydraulic fluid pressure to build thereupon until the actuation sleeve is displaced. The restriction element is retained within the sleeve seat by gravity or while fluid pressure is maintained thereupon. However, conventional reamer designs do not provide positive retention of the restriction element.
A conventional gravel packing tool as generally described in U.S. Pat. No. 6,702,020 entitled “Crossover Tool,” the entire disclosure of which is incorporated by reference herein, provides a sleeve for trapping a ball. The ball is dropped into the tool and lands on a thin sleeve, which acts as the initial ball seat. Upon pressure buildup, the ball is forced past the thin sleeve and into sealing contact with a seat of a second sleeve, which is an extension of the thin sleeve and where both sleeves are retained in the tool. A shear pin holds the second sleeve in its initial position. A snap ring is mounted to the second sleeve and it is able to snap out of its recess allowing the second sleeve shifts as a result of applied fluid pressure upon the ball on the seat and when the fluid pressure is sufficient to shear the shear pins holding the second sleeve in its initial position. As a result of this movement, the internal diameter of the thin sleeve, through which the ball has already been forced, is further reduced as it is pulled through a reduced diameter of a surrounding body and locks the ball into the seat. The ball cannot be dislodged, particularly in the opposite direction, until a predetermined pressure is exceeded. Undesirably, dynamic motion required by the thin sleeve and the second sleeve in order to secure the ball only occurs after sufficient fluid pressure has been applied for shearing the shear pins and releasing the snap ring. Also, a sleeve for trapping a ball of a conventional gravel packing tool is undesirable for use with a downhole tool that includes an actuation sleeve, such as an expandable reamer apparatus, particularly where the actuation sleeve is selectively retained by fluid pressure and release of the actuation sleeve is desired only after the restriction elements is secured.
Furthermore, the shockwave or pressure build-up in order to secure the restriction element may likely initiate premature releasing of an actuation sleeve, rendering the captioning of the restriction element in an indeterminate or unknown state and possible premature tool activation.
Accordingly, it would be desirable to improve the performance of a downhole apparatus, such as an expandable reamer apparatus, by providing positive and robust retention of a restriction element. There is a further desire to provide determinate retention of a restriction element within an actuation element, such as the traveling sleeve of an expandable reamer apparatus. Moreover, there is a desire to provide verifiable retention of a restriction element prior to dynamic release of an actuation element. Lastly, there is a desire to provide positive retention of a restriction element without necessitating dynamically moving parts.